Geo: Relative URL roots in external_url causes redirect loop on secondary login

Summary

Having a relative URL root in the external_url of a primary causes a 302 redirect loop on the secondary when logging in.

Steps to reproduce

1. Set the external_url with a relative root
2. Add secondary
3. Try to login to secondary
4. Gets redirected to primary for login
5. Enter credentials
6. Redirect back to secondary gets stuck in 302 redirect loop

What is the current bug behavior?

external_url with relative URL root (i.e. gitlab.example.com/gitlab) causes a 302 redirect loop when logging into a secondary

What is the expected correct behavior?

You should be redirected back to the secondary after entering credentials.

Relevant logs and/or screenshots

In the secondary NGINX logs we see: multiple 302 for GET /gitlab/oauth/geo/callback? until we see 499

In the primary NGINX logs we see:

==> /var/log/gitlab/nginx/gitlab_error.log <==
2018/03/26 11:00:15 [error] 20783#0: *135 open() "/var/opt/gitlab/nginx/html/api/v4/user" failed (2: No such file or directory), client: 1.1.1.1, server: gitlab.example.com, request: "GET /api/v4/user HTTP/1.1", host: "gitlab.example.com"

==> /var/log/gitlab/nginx/gitlab_access.log <==
172.22.203.18 - - [26/Mar/2018:11:00:15 -0400] "GET /api/v4/user HTTP/1.1" 404 1565 "" "Faraday v0.12.2"

See customer ticket for logs from primary and secondary servers.

Links

Customer ticket -> https://gitlab.zendesk.com/agent/tickets/93087 (internal)

GitLab 10.5.5-ee

customer ~Geo